Naturally occurring tularemia is a zoonotic disease of animals and humans caused by the bacterium Francisella tularensis. Rodents are especially susceptible and often die in large numbers during outbreaks. Humans can become infected through several routes, including: tick and deer fly bites, skin contact with infected animals, ingestion of contaminated water, inhalation of contaminated aerosols or agricultural dusts.
F. tularensis is routinely monitored in environmental sampling undertaken by the National Centre for Disease Control/Lugar Centre. After several years of observation, two principle tularaemia foci were highlighted on the territory of East Georgia: Kartl-Kakheti and Meskhet-Javakheti.
For isolation and detection of specific bacteriophages against F. tularensis, the enrichment method was used. Enrichment was performed in BHI broth supplemented with 0.1% Cysteine, 1% Glucose and a mix of antibiotics. Eight tick samples (Positive by PCR-testing), collected in the region of Kartli in 2014, and environmental samples were used as sources for phage isolation. One vaccine (Ft-LVS) and four virulent strains (Ft-4809, Ft-4812, Ft-6958 and Ft-8932) were used for inoculation. Enriched samples were cultivated for 96 hours at 37°C. Bacteriophages were detected by spot test assay and liquid culture lysis.
Transparent zones appeared on bacterial lawn on CHAB-medium indicating lytic activity of three out of eight tick samples and one environmental sample against corresponding bacterial strains; whereas the lytic activity in liquid media (BHI media supplemented with 0.1% Cysteine) was revealed by six samples in total. Appelman’s method was used to increase the stability and lytic activity of phage lysates in liquid media.
Electron microscopic study of concentrated phage lysates revealed phage particles with different morphology representing two different morphological families: Syphoviridae and Myoviridae.
Several phages with lytic activity against vaccine and virulent bacterial strains of F. tularensis are not stabile, although they reveal strong inhibitory activity against host bacteria in liquid conditions.